Method of fabricating a magnetic memory matrix

ABSTRACT

A method of fabricating a magnetic memory device having spaced, parallel, magnetically coated wires received within tunnels and spaced parallel word conductors crossing the magnetically coated wires at right angles and in close proximity thereto, in which a substrate is formed to have a contoured surface of elongated parallel recesses for receiving the magnetically coated wires and the word conductors are electroplated directly onto the contoured surface of the substrate to follow the shape of the substrate surface. The exposed conductive surfaces of the plated word conductors are then coated with a thin film of insulative material and the completed structure forms one side of the memory that is joined to an identical, similarly formed mating opposite dise.

United States Patent Cole et al.

[54] METHOD OF FABRICATING A MAGNETIC MEMORY MATRIX [72] Inventors: John M. Cole, New Hope, Pa.; William Sinclair, Frenchtown, NJ.

3,042,591 7/1962 Cado ..29/604 UX 3,077,021 2/1963 Brownlow..... 29/604X 2 122: 2ll l6 t*3 5 i !2 .---2 0,4u. 5

Sasaki et al. ..29/604 X Michaud et al. 29/604 3,465,308 9/1969 3,538,599 ll/l970 Primary Examiner-Robert L. Spicer, Jr. Attorney-David Teschner, Esq.

[57] ABSTRACT A method of fabricating a magnetic memory device having spaced, parallel, magnetically coated wires received within tunnels and spaced parallel word conductors crossing the magnetically coated wires at right angles and in close proximity thereto, in which a substrate is formed to have a contoured surface of elongated parallel recesses for receiving the magnetically coated wires and the word conductors are electroplated directly onto the contoured surface of the substrate to follow the shape of the substrate surface. The exposed conductive surfaces of the plated word conductors are then coated with a thin film of insulative material and the completed structure forms one side of the memory that is joined to an identical, similarly formed mating opposite dise.

10 Claims, 5 Drawing Figures Patented July 18, 1972 m5 ma "We w m METHOD OF FABRICATING A MAGNETIC MEMORY MATRIX BACKGROUND OF THE INVENTION This invention relates to electronic memories of the type known as plated wire or magnetic wire matrix memories. Specifically, it concerns an improved method of making such memories.

Increasing use has been made of the magnetic wire storage matrix since its comparatively recent introduction. Such a matrix includes a series of spaced parallel wires coated with a magnetic substance and an orthogonal series of spaced parallel word conductors, or lines, which cross the magnetically plated conductors in close proximity. One of the prime advantages of these devices is the ease with which the bit word capacity of the matrix may be done very dense. That is, a great number of both word lines and memory elements may be located within a very small area. However, with increasing density, it becomes important to manufacture the matrix to especially close tolerances. In this same connection, it is known that the word conductors and the magnetically coated wires should cross in very close proximity in order to enhance reliability and obtain satisfactory efficiency. Thus, the better the electromagnetic coupling between the magnetically coated wires and the word lines, the better is the efficiency and the less is the current which must be injected in order to either write in or to read out information stored on the magnetically coated wire. Ideally, therefore, the word line completely surrounds the magnetically plated wire, although electrically insulated therefrom by a thin insulative layer.

At first, storage matrices of this type were manufactured by weaving techniques, much like the techniques used in weaving cloth. Thus, the word lines and the magnetic elements became the warp and weft threads of the magnetic storage fabric. This fabric, understandably, must be manufactured with extreme care, owing to the fragility of the wires and the sensitivity of the magnetic plating. To protect the fabric after it has been woven, it is generally coated with a sheet of flexible plastic material. Because of the delicacy of the waving operation and the susceptibility of the magnetically plated wires and the word conductors to inadvertent damage, other techniques for forming magnetic matrices were developed.

In one such technique, the weaving step was eliminated al together by laminating tunnel wires" between two thin sheets of laminate. These tunnel wires are used only for the purpose of forming tunnels within the laminate and, after lamination of the sheets, they are withdrawn to form fine cylindrical tunnels. Thereafter, the magnetically plated (or bit) wires are inserted in the tunnels formed by the withdrawn tunnel wires. Following that step, word straps are laminated to a thin film, with the underside of the straps being either exposed or sometimes also covered with a thin insulating film. In this form, the word straps are wrapped around the tunnel structure containing the bit wires and bonded to the tunnel structure with an adhesive. Although this method eliminates the weaving step, the tunnel structure support does not always permit the location of the word straps in optimum proximity to the magnetic elements. Moreover, several lamination steps are required and this entails certain risk that delicate conductors may be ruined.

Other methods forming the matrices thus found their way into use. Among those is the method in which grooves are formed or cut into a substrate and the magnetic elements laid into the grooves. Word straps in a flexible insulative sheet are wrapped around the substrate to overlie the magnetic wires and form the matrix. In one alternative of this method, word straps are etched onto a second substrate that is subsequently joined to the first so that the word straps are perpendicular to the laid-in bit wires. Among the problems of this method are the precautions required to maintain the bit wires in the grooves and the difliculty of forming the grooves with extremely small spacing and to the uniformity required to obtain reliable and consistent output potential when the identical current is supplied to each of the many word straps.

These methods were greatly improved upon in the process described in the co-pending application Ser. No. 73,654 of Joseph W. Breakfield for Memory Storage Unit and Method of Making Same, assigned to the assignee of the present invention. According to that method, a flat laminate containing the word straps is molded directly and intimately around the tunnel wires.

The present invention represents yet another improvement in the art of constructing magnetic computer memory matrices and has substantial advantages in several respects over individual ones of the prior art methods. First, a rigid memory structure can be formed because the method implements a molded epoxy substrate. Second, the use of an epoxy resin or similar molded material as a sulxtrate enables the accurate location of recesses that are to receive the memory elements. Among the most important advantages of the method is that it makes possible the location of word straps in very close proximity to the magnetic elements. In fact, the word straps can be separated from the memory elements only by a thin film of dielectric insulation so that they completely surround the bit lines.

The present method results in a magnetic memory device similar in structure to the memory disclosed in U. S. Pat. No. 3,460,l 13 to I-Iisao Maeda, wherein the memory is formed by bonding onto a magnetic insulating base plate (similar to the one used in the present invention) an insulating sheet carrying a series of embedded parallel word straps. In this method, special machinery such as a toothed or splined roll must be used to press the word strap sheet into registration with grooves formed in the insulating base plate, and this operation must be carried out with a great deal of precision because of the close spacing between adjacent bit lines.

SUlVIMARY OF THE INVENTION The present invention constitutes an improvement and a new approach to the fabrication of magnetic memory matrices and allows the location of word lines in close proximity to the memory elements in a precise and reliable manner. To this extent, the invention overcomes many of the disadvantages of the prior art methods in which either the word lines cannot be positioned to completely surround all or a major portion of the magnetic element surfaces or cannot economically or easily obtain high word and bit line density.

These and other advantages of the invention are accomplished by providing a insulative substrate having one surface contoured with a series of parallel grooves to receive magnetic elements, and selectively plating the contoured surface to form a series of word conductors following the contoured surface in intersecting relationship. In a preferred form of the invention, a mating substrate having a similar series of parallel recesses is plated and joined to the other substrate so that the recesses of each are aligned to form a series of parallel tunnels for receiving the memory wires.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, the following detailed description of the preferred embodiment of the invention and the drawings may be referred to. In those drawings:

FIG. I is the perspective view of a suitable substrate for use in the invention;

FIG. 2 is a perspective view of the substrate after it has been coated with a conductive layer;

FIG. 3 is a perspective view of the plated substrate after selective etching forming a series of orthogonal word conductors;

FIG. 4 is a perspective view of a magnetic matrix tunnel structure formed by joining identical substrates of the type il lustrated in FIG. 3; and

FIG. 5 is a cut-away, slightly enlarged, perspective view of the FIG. 4 structure, illustrating also the magnetic elements positioned within the tunnels of the basic structure.

DESCRIPTION OF THE PREFERRED ENIBODHWENT OF THE INVENTION FIG. 1 illustrates a substrate suitable for use in the invention. The substrate 11, or base, is formed with a series of semicylindrical recesses 13 which, when the memory matrix is completed, receive the memory elements. Preferably, the unit 1 l is a rigid structure; however, it is within the scope of the invention to have the substrate formed from a flexible material, and to have recesses of other than semicylindrical cross-sec tion. Among the materials suitable for forming the base 11 is glass reinforced, partially cured epoxy. This material can be compression molded in a metal mold having raised contours to form the recesses 13, and during the molding process, the partially cured epoxy becomes fully cured.

Following formation of the basic unit 11, its contoured surface 15 is printed (plated) with a conductive layer or film 17. For example, the surface may be electroplated using techniques known in the printed circuit board art. The substrate following plating with the layer 17 of conductive materials is shown in FIG. 2. It should be observed that the conductive plate 17 follows the contours of the grooves of 13.

Since the conductive layer 17 is to provide the word lines for the magnetic memory, the thickness of the plate 17 will depend upon the desired electrical characteristics of the matrix. Depending on the width of the word lines (and this in turn will depend somewhat on the desired physical word line density), the thickness of the plate will be selected for its resistance and other distributed electrical characteristics. The word line pitch, on the other hand, can be varied to satisfy minimum performance requirements of inter-line cross-talk and to minimize other types of interference and spurious signal sources.

To form the separate word lines, the upper surface of the copper plate is coated with a photo-sensitive resist and covered with a contoured transparent mask having an opaque conductor pattern that is exposed to illumination. The undeveloped resist is then removed by washing and the copper plate is etched to leave a pattern of continuous contoured conductors on the top surface. The structure of the matrix following this etching step is illustrated in HG. 3, where the conductors 19 formed from etchingthe solid state 17 can be clearly seen. The interstices 21 between adjacent conductors 19, left after etching, are those areas where the exposed photosensitive resist areas were etched. These spaces 21 may, if desired, be filled with either a dielectric material and/or material having also a high magnetic permeability to maximize the flux coupling with the magnetic bit lines.

As noted earlier, the preferred method incorporates two contoured substrate units like that shown in FIG. 3 so that the aligned recesses 13 of the two mated etched substrates form a series of spaced parallel tunnels 22. The resultant structure, illustrated in FIG. 4, shows a mating plate 11a placed on top of the plate 11. Prior to mating these two sections 11, 11a, the exposed upper surfaces of the word straps 19 are coated with a thin dielectric film, designated by the numeral 24 in FIGS. 4 and 5. The mated individual conductors 19 on each substrate. When interconnected at one end form a conductor loop around each of the memory elements to be inserted in the tunnels 22. The final structure is shown in FIG. 5.

Referring to FIG. 5, the final matrix assembly includes the mated units 11, 11a, each identically formed with a series of spaced parallel word straps 19, on the mating surface each of which is a thin but highly dielectric coating 24 of insulation. Spaces 21 are left between adjacent word straps 19, but these may be filled with a suitable dielectric or magnetically permeable material. At this juncture, it should be remarked that the two substrates may be mated in any suitable manner. For example, the plate halves may be bonded or removably joined by screws, clips, or other mechanical fasteners.

FIG. also illustrates the magnetic elements 26 which have been inserted into the tunnels 22. The magnetic elements 26 comprise a round wire conductor 27 and surrounding magnetic coating 29, as is well known. The word straps 19, as it will be seen, are intimately proximate to the magnetic coating 29 and, in fact, form nearly a perfect conductor turn around the magnetic coating.

Because of the method of fabricating the magnetic matrix, the word straps 19 can be laid down within the recesses 13 with substantial precision. Further, it is also possible to insert tunneP wires in the tunnels 22 during the mating process both for the purpose of alignment and to-avoid damage to the plated wires, since the magnetic wires 26 can be laid into the recesses 13 prior to mating of the two sections 11, 110, the possibility of damaging the magnetic elements is minimized, because they do not have to be drawn through the tunnels 22, as is the case with some of the prior art methods already discussed.

From the foregoing description it is seen that the invention provides the advantages of using a flexible or rigid insulative matrix structure, accuracy in the location of word lines, use of known photosensitive and etching techniques, and the possibility of locating the word lines and the magnetic elements in close proximity to each other and also with the word lines surrounding nearly of the circumferential distance around the magnetic element. Moreover, this method of fabrication offers the alternatives of laying the magnetic elements into the parallel recesses prior to mating of the adjoining sections or of forming tunnels either with or without removable tunnel wires.

It is evident that the invention may be practiced with numerous variations, both of the type discussed and others that would readily occur to both those skilled in the art. For example, the conductive plate may be formed on the substrate surface by bonding as well as by vacuum deposition and electroplating. Also, other etching techniques can be applied to form the ultimate word conductors. All such variations or similar modifications are intended to be included within the scope of the appended claims.

What is claimed is: 1. A method of fabricating a magnetic memory device of the type having a first series of spaced parallel memory elements and a second series of spaced parallel word conductors crossing the memory elements in close proximity thereto, the steps of:

forming a substrate having a contoured surface including a series of elongated parallel recesses for receiving at least a portion of the memory elements;

plating the entire contoured surface of the substrate to form a like contoured metal plate thereon;

treating the metal plate with a photosensitive resist;

exposing selected areas of the coated metal plate; and

removing the underexposed areas of the resist-coating metal plate to leave on the contoured surface the spaced series of word conductors conforming to the contoured surface in intersecting relationship.

2. A method as defined in claim 1, further comprising:

forming a mating substrate having a series of elongated parallel recesses; and

joining the mating substrate to the plated substrate to have the recesses in alignment and thereby form a series of parallel tunnels for receiving the memory elements.

3. A method as defined in claim 2, ftuther comprising:

inserting into the parallel tunnels a series of magnetically polarizable conductors.

4. A method as set forth in claim 3 further comprising:

plating the mating substrate in the same manner as the first substrate prior to joining the two substrates in mating relationship.

5. A method as defined in claim 1, further comprising:

coating the exposed surfaces of the plated word conductors with a dielectric film.

6. A method according to claim 1, in which the exposure step includes:

placing over the resist-coated plate a mask having a series of opaque areas in the pattern to be formed by the word conductor series; and

illuminating the mask to expose the resist.

7. A method as defined in claim 1, in which:

the substrate is formed by simultaneously heating and compressing in a mold a partially cured epoxy substance that cures upon the application of heat and pressure.

8. A method of making a magnetic memory plane of the type having intersecting series of parallel word and bit lines, comprising:

forming a flat insulative base having in one flat surface thereof a series of spaced substantially parallel recesses; forming integrally on said surface a series of thin, flat parallel word conductors, said word conductors intersecting and following the surface contour of said recesses; and

placing in said recesses magnetically coated bit conductors electrically insulated from said intersecting word conductors. 9. A method as set forth in claim 8, in which the word con- 5 ductors are made by:

forming a thin conductive plate on the substrate, the plate following the contour of the one surface; and

selectively removing portions of the plate to leave the word conductors.

10. A method in accordance with claim 9, wherein:

portions of the conductive plate are removed by etching.

* i i l 

1. A method of fabricating a magnetic memory device of the type having a first series of spaced parallel memory elements and a second series of spaced parallel word conductors crossing the memory elements in close proximity thereto, the steps of: forming a subStrate having a contoured surface including a series of elongated parallel recesses for receiving at least a portion of the memory elements; plating the entire contoured surface of the substrate to form a like contoured metal plate thereon; treating the metal plate with a photosensitive resist; exposing selected areas of the coated metal plate; and removing the underexposed areas of the resist-coating metal plate to leave on the contoured surface the spaced series of word conductors conforming to the contoured surface in intersecting relationship.
 2. A method as defined in claim 1, further comprising: forming a mating substrate having a series of elongated parallel recesses; and joining the mating substrate to the plated substrate to have the recesses in alignment and thereby form a series of parallel tunnels for receiving the memory elements.
 3. A method as defined in claim 2, further comprising: inserting into the parallel tunnels a series of magnetically polarizable conductors.
 4. A method as set forth in claim 3 further comprising: plating the mating substrate in the same manner as the first substrate prior to joining the two substrates in mating relationship.
 5. A method as defined in claim 1, further comprising: coating the exposed surfaces of the plated word conductors with a dielectric film.
 6. A method according to claim 1, in which the exposure step includes: placing over the resist-coated plate a mask having a series of opaque areas in the pattern to be formed by the word conductor series; and illuminating the mask to expose the resist.
 7. A method as defined in claim 1, in which: the substrate is formed by simultaneously heating and compressing in a mold a partially cured epoxy substance that cures upon the application of heat and pressure.
 8. A method of making a magnetic memory plane of the type having intersecting series of parallel word and bit lines, comprising: forming a flat insulative base having in one flat surface thereof a series of spaced substantially parallel recesses; forming integrally on said surface a series of thin, flat parallel word conductors, said word conductors intersecting and following the surface contour of said recesses; and placing in said recesses magnetically coated bit conductors electrically insulated from said intersecting word conductors.
 9. A method as set forth in claim 8, in which the word conductors are made by: forming a thin conductive plate on the substrate, the plate following the contour of the one surface; and selectively removing portions of the plate to leave the word conductors.
 10. A method in accordance with claim 9, wherein: portions of the conductive plate are removed by etching. 